Re: Digital Camera Resolution WAS: Warning of major NHS IT overspend

[Brian Gladman <[EMAIL PROTECTED]>]

Brian Beesley wrote:
> On Thursday 04 November 2004 10:59, Brian Gladman wrote:
>
> > Brian Beesley wrote:
> >
> > > On Tuesday 02 November 2004 18:08, Brian Morrison wrote:
> > >
> > > > On Tue, 02 Nov 2004 16:46:44 +0000 in [EMAIL PROTECTED]
> > > >
> > > > Brian Gladman <[EMAIL PROTECTED]> wrote:
> > > >
> > > > > High end digital compact cameras do not have such small sensors. The
> > > > > one I use has a 16mm square sensor with 8 Mpixels.  This works out at
> > > > > about 1/3 the area of a 35mm frame and provides a resolution of about
> > > > > 170 pixels/mm.
> > >
> > > Check it, I think you're more likely to find it's 16 square millimetres
> > > than 16 millimetres square.
> >
> > In the documentation it is specified as a "2/3 inch CCD" with 8M pixels.
> >
> > If this is 2/3 square inch it would be 20mm x 20mm (or a rectangle of
> > the same area); if it is 2/3 inch x 2/3 inch it would be 17mm by 17mm.
>
>
> Common misconception. "2/3 inch" is an anachronism; the value refers to the 
> _external_ dimension of the _diagonal_ of the vidicon tube, when TV cameras 
> were made that way. Like the description of the screen size of a TV set, only 
> with small sensors the deficit is proportionately much greater.
>
> "2/3 inch" sensor is approx. 7mm x 5mm active area.

That sounds logical (although naughty on the part of CCD manufacturers).

The specification of my cameras zoom lens - 8.9mm to 89mm - is said to 
be equivalent to 35mm to 350mm on a 35 mm camera, a ratio which suggests 
a sensor area of 6mm x 9mm, 1/16 the area of a 35mm image.

This gives an image plane resolution of about 400 pixels/mm. The smaller 
area makes the task of the lens much easier but the resolution 
requirement is also higher so it is not immediately obvious which will 
limit the resolution.

   Brian Gladman